Turbines operating in highly pulsating gas flows may need additional damping/stiffness in order to ensure their survival. This additional damping/stiffness can be provided by inserting a lacing wire through holes in the turbine blades to tie them together and support them during operation.
However, during operation the lacing wire applies an inertial load which produces stresses in the blades. To prevent these stresses from becoming excessive, a boss may be added around the hole in each blade.
The boss is a local thickening of the aerofoil section of the blade, which reduces the stresses produced in the blade by the inertial load of the wire. For example, FIG. 1 shows neighbouring industrial turbocharger turbine blades 1 with a lacing wire 3 inserted through holes 5 in the aerofoil bodies 7 of the blades. A boss 9 surrounds each hole and supports the wire.
Although the boss reduces stresses in the blade, it also disrupts the flow of a gas stream over the aerofoil body and thus reduces the efficiency of the blade.